I had the same problem after I took mine apart. There was no daylight when it was assembled but after shooting it for a while there is a small gap. I thought I did something wrong. I bought another gun for cowboy action shooting and this one is starting to showing a small gap also. I didn't have this one apart.
It doesn't affect anything but it bugs me.
I put just a little bit of thread lock where the sail meets the frame, and there's been no gap. I also put some thread lock on the screw that holds the assembly in place. The gun heats up enough when I shoot to where complete disassembly is easy within an hour or two after I shoot, so for now I'd consider it a successful fix, at least until I can get the gun to someone who can provide a more long term solution. I do agree, it never affected performance, but it is irritating.